Coated articles are known in the art for use in window applications such as insulating glass (IG) window units, vehicle windows, monolithic windows, and/or the like. In certain example instances, designers of coated articles often strive for a combination of high visible transmission, substantially neutral color, low emissivity (or emittance), low sheet resistance (Rs) low U-values in the context of IG window units, and/or low specific resistivity. High visible transmission and substantially neutral color may permit coated articles to be used in applications where these characteristics are desired such as in architectural or vehicle window applications, whereas low-emissivity (low-E), low sheet resistance, and low specific resistivity characteristics permit such coated articles to block significant amounts of IR radiation so as to reduce for example undesirable heating of vehicle or building interiors.
Consider a typical coated article with the following layer stack. This coated article is suitable for use in an IG (insulation glass) window unit. For the coated article listed below, the coating includes layers that are listed from the glass substrate outwardly.
LayerThickness (Å)GlassTiOx140 ÅSnOx100 ÅZnAlOx 70 ÅAg118 ÅNiCrOx 20 ÅSnOx223 ÅSiNx160 Å
The silver (Ag) layer of the above coated article has a thickness of 118 angstroms (Å) and a sheet resistance (Rs) of 4.6 ohms/square. This translates into a specific resistivity (Rs multiplied by thickness of the IR reflecting layer) for the silver IR reflecting layer of 5.43 micro-ohms·cm.
While the aforesaid specific resistivity (SR) of the silver IR reflecting layer is adequate in many situations, it would be desirable to improve upon the same. For example, if the above coated article is heat treated (e.g., thermally tempered), it does not have good thermal stability. In other words, such heat treatment (HT) causes optical properties of the coated article (e.g., one or more of a*, b*, L*, haze) to substantially change in an undesirable manner. If the a*, b* and/or L* values change too much upon HT of the coated article, then the coated article is said to be thermally unstable since it looks much different after HT than before HT. Moreover, if emissivity and/or sheet resistance (Rs) goes up too much upon HT, then the product is also said to be thermally unstable.
U.S. Patent Document 2005/0042460 (the disclosure of which is hereby incorporated herein by reference) discloses a layer stack that is suitable in many different instances, where the zinc oxide layer contacts the underside of the silver IR reflecting layer. It has been found that when the zinc oxide directly contacts the bottom side of the silver, in certain instances the haze and/or sheet resistance of the coating rise too much upon HT.
In view of the above, it will be appreciated that there exists a need in the art for a coated article including a coating which has good thermal properties (e.g., emissivity/emittance and sheet resistance), good optical properties (e.g., a*, b* and/or L*), and which has such good thermal and optical properties following heat treatment such as thermal tempering. Certain example embodiments of this invention relate to a coated article which permits one or more of these advantages to be realized.
In certain example embodiments of this invention, it has surprisingly been found that the provision of a layer stack including the following sequence of layers, moving away from the glass substrate, is advantageous: (a) a layer of or including silicon nitride, (b) a layer of or including zinc oxide, (c) a layer of or including an oxide of Ni and/or Cr, and (d) an IR reflecting layer. This sequence of layers permits the coated article to realized improved thermal stability. Thus, the coated article's color, haze, emittance and sheet resistance do not change in an undesirable manner due to heat treatment (HT). For example the emittance and/or sheet resistance does not rise substantially (but may decrease) upon HT, and/or the coated article does not becomes too hazy due to HT. In certain example embodiments layers of or including titanium oxide (and possibly tin oxide) may be provided under and contacting the layer comprising silicon nitride.
In other example embodiments of this invention, it has surprisingly been found that the following sequence of layers is advantageous: (a) a layer of or including tin oxide, (b) a layer of or including zinc oxide, (c) a layer of or including an oxide of Ni and/or Cr, and (d) an IR reflecting layer (e.g., silver inclusive layer). This sequence of layers permits the coated article to realized improved thermal stability. Thus, the coated article's color and haze do not change in an undesirable manner due to HT. For example, the a*, b* and/or L* values do not change too much upon HT, and/or the coated article does not becomes too hazy due to HT.
In certain example embodiments of this invention, the zinc oxide inclusive layer may be formed by sputtering a ceramic target. It has been found that implementing a zinc oxide inclusive layer formed using a ceramic target, beneath a layer comprising an oxide of Ni and/or Cr, yields an improvement in the quality of the overlying silver inclusive IR reflecting layer. This structure has also been surprisingly found to provide a greater degree of thermal stability during HT compared to the use of zinc oxide alone as the seed layer under the silver.
In certain example embodiments of this invention, it is especially surprising that such advantages can be realized in a single IR reflecting layer coating (e.g., single silver coating) that is also able to realize, when used in an IG (insulating glass) unit, a U-value of no greater than 1.25 W/(m2 K), more preferably no greater than 1.20 W/(m2K), even more preferably no greater than 1.15 W/(m2K), and most preferably no greater than 1.10 W/(m2K).
In certain example embodiments of this invention, there is provided a heat treated coated article including a coating supported by a glass substrate, the coating comprising: a dielectric layer; a layer comprising silicon nitride; a layer comprising zinc oxide over and directly contacting the layer comprising silicon nitride; a layer comprising an oxide of Ni and/or Cr over and directly contacting the layer comprising zinc oxide; an infrared (IR) reflecting layer comprising silver on the glass substrate, located over and directly contacting the layer comprising an oxide of Ni and/or Cr; another layer comprising an oxide of Ni and/or Cr located over and directly contacting the IR reflecting layer comprising silver; a layer comprising a metal oxide located over and directly contacting the another layer comprising the oxide of Ni and/or Cr; and a layer comprising silicon nitride located over the layer comprising the metal oxide.
In other example embodiments of this invention, there is provided a coated article including a coating supported by a glass substrate, the coating comprising, from the glass substrate outwardly: a layer comprising silicon nitride or tin oxide; a layer comprising zinc oxide over and directly contacting the layer comprising silicon nitride or tin oxide; a layer comprising an oxide of Ni and/or Cr over and directly contacting the layer comprising zinc oxide; an infrared (IR) reflecting layer comprising silver over and directly contacting the layer comprising an oxide of Ni and/or Cr; and a dielectric layer.
In other example embodiments of this invention, there is provided a method of making a coated article, the method comprising: providing a glass substrate; forming a layer comprising silicon nitride or tin oxide on the glass substrate; sputtering a ceramic target comprising zinc and oxygen in an atmosphere including at least an inert gas in order to form a layer comprising zinc oxide on the glass substrate over and directly contacting the layer comprising silicon nitride or tin oxide; forming a layer comprising an oxide of Ni and/or Cr on the glass substrate over and directly contacting the layer comprising zinc oxide; forming an infrared (IR) reflecting layer comprising silver on the glass substrate over and directly contacting the layer comprising an oxide of Ni and/or Cr; and forming a dielectric layer over at least the IR reflecting layer.